Dehydration may be associated with increased risk of developing dental disease, urinary tract infections, broncho-pulmonary disorders, kidney stones, constipation, poor immune function, cardiovascular pathologies, and impaired cognitive function. The maintenance of body fluid balance may often be one of the foremost concerns in the care and treatment of critically ill patients, yet physicians have access to few diagnostic tools to assist them in this vital task. Patients with congestive heart failure, for example, frequently suffer from chronic systemic edema, which must be controlled within tight limits to ensure adequate tissue perfusion and prevent dangerous electrolyte disturbances. Dehydration of infants and children suffering from diarrhea can be life-threatening  if not recognized and treated promptly.
The most common method for judging the severity of edema or dehydration is based on the interpretation of subjective clinical signs (e.g., swelling of limbs, dry mucous membranes), with additional information provided by measurements of the frequency of urination, heart rate, urea nitrogen (BUN)/creatinine ratios, and blood electrolyte levels and/or protein levels. None of these existing single-variable assessments, however, provide a means to easily determine water retention or loss.